Many types of coatings may be applied on a base material. Electrodeposition is a common technique for depositing such coatings. Electrodeposition generally involves applying a voltage to a base material placed in an electrodeposition bath to reduce metal ionic species within the bath which deposit on the base material in the form of a metal, or metal alloy, coating. The voltage may be applied between an anode and a cathode using a power supply. At least one of the anode or cathode may serve as the base material to be coated. In some electrodeposition processes, the voltage may be applied as a complex waveform such as in pulse plating, alternating current plating, or reverse-pulse plating.
A variety of metal and metal alloy coatings may be deposited using electrodeposition. For example, metal alloy coatings can be based on two or more transition metals including Ni, W, Fe, Co, amongst others.
Corrosion processes, in general, can affect the structure and composition of an electroplated coating that is exposed to the corrosive environment. For example, corrosion can involve direct dissolution of atoms from the surface of the coating, a change in surface chemistry of the coating through selective dissolution or de-alloying, or a change in surface chemistry and structure of the coating through, e.g., oxidation or the formation of a passive film. Some of these processes may change the topography, texture, properties or appearance of the coating. For example, spotting and/or tarnishing of the coating may occur. Such effects may be undesirable, especially when the coating is applied at least in part to improve electrical conductivity since these effects can increase the resistance of the coating.